Feed-back circuits



July 1, 1947. J. R. BANKER 2,423,362

FEED BACK CIRCUITS Filed April 24, 194:

MAAAAAAAA M Q QINVENMR.

FITTO/PNEY grid leak 22.

Patented July 1, 1 947 FEED-BACK CIRCUITS John Richard Banker, Passaic, N. J assignor to Allen B. DuMont Laboratories, Inc., Passaic, N. J., a corporation of Delaware ApplicationApril'24, 1943,Serial No. 484,497

,1 41Claims. (01. 179-471) This invention relates to a device for obtaining an alternating current or voltage wave of a desired sort from a complex wave which contains one or more undesired waves as components.

The invention will be described particularly by I way of an illustrative example of how to remove an undesired sawtooth component of a given Wave so as to result in an output signal of the desired square wave shape.

The invention may be understood from the description in connection with the accompanying drawing showing a diagram of connections.

In the drawing, reference character I indicates a vacuum tube having an input terminal 2 to which a complex wave such as the square wave 3 is fed and applied to the grid 4 that is provided with the grid leak 5. The cathode 6 of tube is connected to the plate of tube I, the cathode 8 of which is loaded with resistance 9.

A source of voltage I2 applies positive potential to the plate of tube and negative potential to the resistance 9. A condenser|3 couples the cathode 6 to the grid of tube I4 that is provided with grid leak resistance l5. Positive Potential is applied through load resistance It to the plate of tube I4 and the cathode of this tube is connected through resistance IT to ground to bias this cathode. A condenser 20 couples the plate of tube I4 to the grid of tube 2| which is provided with Resistances 23 and 24 in series are connected between the positive side of the potential I2 and plate of tube 2| and a resistance 25 interposed between the cathode of this tube and ground. A lead 28 with condenser 3|lcouples a point between resistances 23 and 24 to one end of a resistance 29. The other end of this resistance 29 is connected to the negative side of source |2. The resistance 29 is provided with a sliding contact 3| which is connected by lead 32 to the grid of tube 1.

A condenser 23 is connected from lead 28 to ground on the side of condenser 30 opposite resistance 29, and the output lead 35 from the device is connected to the plate of tube 2|.

The operation is as follows: When a signal such as the square wave 3 of voltage is applied to the grid 4, signals as shown at 38 and 39 are produced. The distortion of the horizontal portions of signal 38 is due to the time constant of the condenser I3 and resistance combination and that of the amplifiedsignal 3 9- is due to the time constant of condenser 29 and resistance 22.

Application of signal 39 to the grid of tube 2| causes a triangular wave to be produced as shown atfiil. This triangular wave is coupled by lead 28, condenser 30 and lead 32 to the grid of tube 1 in phase such as to add to the signal at 38 so that the sawtooth component is reduced in magnitude. In this way the coupling values of condensers l3 and 29 and resistances I5 and 22 can begreatly reduced in value while still maintaining good response for low frequency components of the original signal 3. I

When the rapidly decreasing voltage of signal .39, represented by the first downwardlyextending vertical line is fed to the grid of tube 2| the current through tube 2| suddenly decreases causing a sudden increase of potential on lead 35 as indicated by the first vertical line in signal 4|. Whenthe voltage of signal 39 isv increasing, as indicated by the upwardly sloping line at the bottom of the signal 39, an increasing voltage is being applied to the grid of tube 2| tending to cause the output voltage on lead 35 to decrease in phase opposition as is usual with amplifier tubes. I-Iowever, the corresponding increase in voltage applied during the time represented by this upwardly sloping portion of signal 39 together with the very rapid rise of potential represented bythe vertically extending portion that follows tend to cause the potential on lead 35 to decrease suddenly, but the voltage supplied by the condenser 33 discharging during this interval of increasing potential on the grid of tube 2| maintains the potential on lead 35 constant during this time interval as represented by the first horizontal line in signal 4 and so on in a similar way while the device is in operation.

As shown by tests with an oscilloscope, when the first rapidly decreasing voltage of signal 39, represented by the first downwardly extending vertical line is fed to the grid of tube 2| the current through tube 2| suddenly decreases causing an increase of the potential at the junction of resistors 23 and 24 as shown by the first upward sloping line of wave form 40. This causes the condenser 33 to charge through the resistor 23, this prevents the potential on the lead 28 from rising as rapidly as the voltage on the lead When the voltage of signal 39 is increasing, as indicated by the upwardly sloping line at the bottom of the signal 39, an increasing voltage is being applied to the grid of tube 2| tending to cause the output voltage on lead 28 to decrease in phase opposition as'is usual with amplifier tubes. The rate of this reduction is determined by thev rate of discharge through resistor 24. This discharge continues through the upwardly the amplitude of the triangular wave applied to the grid of tube 1 in a convenient way.

What is claimed is:

1. A feed back circuit, comprising a vacuum tube to the grid of which "a 's'i'gnailis appliet, =asecond vacuum tube having "a"reslstancein itsf cathode circuit and having its plate connected to the cathode of said first tube, an amplifier coupled to the connection between said tubes, and

a connection from the plate circuit of sarcasm-'- plifier to the grid of said second vacuum tube.

'2 The device Of cluim- 1, ii-1 said last named connection meiudesa 'Sistanc'e;

3. The I'lvi'oe of claim -1,-- ir1- Wh-iCh S9;id l'as't nam'e'd connection includes a resi'stance anda eondenser inseries.

4. The device Of "claim 1, in Which-said last named connect-ion includesa Variable --r'esistar'1ce.

'5; 'A- feed-back circuit, comprising-- a vacuum tube to the grid of which a si'g'rial is applied a 's'e'co'nd' vacuum tube having a resistance in its cathode-circuit and its plate connected to the cathode of said first tube, an amplifier comprising apluralit y of vacuum 'tubes coupled to the connection between said tubes ,-aconneotionfrom *the plate circuit of said amplifier'to the grid of saitf'second-"Vacuumtube; a'fid anoiltpllt-lead 00hnecte'd't'o the plate of the last one of said plu- "r ality of 'vacuu'rntubes.

6. Thedeviceof claim fi, in "which aresistance is located in the "plate circuit bit Said amplifier and the output connection from said device is taken ofibetWeen-the plate'o'f said-amplifier-and said last named resistance.

'7. menswear-claim 5, in whicha resis'tan'ce is located in the plate circuit of said amplifier and the -output connection from said device is taken off between the plate-ofsaid amplifierand "said last named resistance and a resistahce is located between a source of potential and said last named resistance. I

'8; Inadeviceof the character described; two

immber ode connected to the plate of the second one, an input circuit for said first tube, an amplifier having its control grid coupled to said plate and cathode, a second amplifier having its control grid coupled to the plate of said first named amplifier and having its plate coupled to the grid of said second named vacuum tube and an output circuitcou-pl'e'd to the plateof said second named amplifier.

9. The device of claim 8, in which said first tube has its plate connected directly to a source of vpositive potential.

10. The device of claim 8, in which said second tube: has its cathode connected to a source of negative potential;

The-device of claim 8, in which said first 'namedamplifier has its cathode biased by a resistance.

1 2; The'device of claim 8, in which said second named amplifier has a resistance between its plate and the'gridloflsaidsecondcnamed amplifier.

":13. The device of 'claim 8,'in' which said second naniedemplifier-has avariable resistance between it's iplate and the zg'lid Of saidsecond named amplifier.

7 "l4. The'dev ice' of 'iclaim 8, in which said second named amplifier has a resistance between its :plate and the zgridof saidxsecond named amplifier and also has a resistance'between.saidilast named resista'noeand asource of-positive potential. V

UDHN RICHARD BANKER.

ennnrtmions emen 7 v The following references are-of record in the file 6f thispatent':

UNITED s'iWrs PATENTS FOREIGN PATENTS" Country Date G fe' kit-Brit Bin e-Jedi June "1-9, 4,934

Number 2g35'8,4 28 2332656 14 2',243;4I2 2521 7367 2i-l90g482 2}l03,'490 232053007 252 10,390 

